About the Flu

There are two types of vaccines that protect against the flu. The "flu shot" is an inactivated vaccine (containing killed virus) that is given with a needle, usually in the arm. The flu shot is approved for use among people 6 months of age or older, including healthy people and those with chronic medical conditions (such as asthma, diabetes, or heart disease). A different kind of vaccine, called the nasal-spray flu vaccine (sometimes referred to as LAIV for Live Attenuated Influenza Vaccine or FluMist®), was approved in 2003. The nasal-spray flu vaccine contains attenuated (weakened) live viruses, and is administered by nasal sprayer. It is approved for use only among healthy* people 2-49 years of age who are not pregnant.

Each of the two types of vaccine contains three influenza viruses, which are chosen based on information about recently circulating strains. Each of the three vaccine strains in both vaccines - one A (H3N2) virus, one A (H1N1) virus, and one B virus - are representative of the influenza vaccine strains recommended for that year. Viruses for both vaccines are grown in eggs.

How do flu vaccines work?

Both flu vaccines (the flu shot and the nasal-spray flu vaccine (LAIV)) cause antibodies to develop in the body. These antibodies provide protection against influenza virus infection.

When should I get a flu vaccination?

CDC recommends that people get their flu vaccine as soon as vaccine becomes available in their community. Vaccination before December is best since this timing ensures that protective antibodies are in place before flu activity is typically at its highest. CDC continues to encourage people to get vaccinated throughout the flu season, which can begin as early as October and last as late as May. Over the course of the flu season, many different influenza viruses can circulate at different times and in different places. As long as flu viruses are still spreading in the community, vaccination can provide protective benefit.

In addition, there are other people who may benefit from vaccination as late or April or May, even if influenza viruses are no longer circulating in the United States. This includes:

• 1. Persons likely to be traveling to the Southern Hemisphere where influenza may be circulating before the 2009-10 vaccine is available, and
• 2. Children younger than 9 being vaccinated for the first time who still have not received their second recommended dose of vaccine. (If they get their second dose, then they will only need one dose of vaccine next season. If they do not get their second dose, they will still need to get two doses of vaccine the next season in order to best be protected by the vaccine. This is because studies have shown that two doses are needed in children younger than 9 the first year they are vaccinated in order to maximize the protective benefit from vaccination.)

Once you get vaccinated, your body makes protective antibodies in about two weeks. However, children younger than 9 years old who are being vaccinated for the first time still need a second dose 4 or more weeks later in order to be protected.